Stretchable polymeric fibers and articles produced therefrom

ABSTRACT

A stretchable synthetic polymer fiber comprises an axial core formed from an elastomeric polymer, and two or more wings formed from a non-elastomeric polymer attached to the core. The fiber has a substantially radially symmetric cross-section. Such fibers can be used to form garments, such as hosiery.

RELATED APPLICATIONS

[0001] This application claims priority of U.S. Provisional PatentApplications 60/236,144 and 60/236,145, both filed Sep. 29, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to stretchable fibers, includingmultiwing, stretchable synthetic polymer fibers formed from at least twotypes of polymers. The invention also relates to methods of producingsuch fibers. The invention also relates to articles formed from thefibers, including yarns, garments, and the like.

[0004] 2. Description of Related Art

[0005] It is desired to impart stretchability into many products formedfrom synthetic fibers, including various garments, such as sportswearand hosiery.

[0006] As disclosed in U.S. Pat. No. 4,861,660 to Ishii, various methodsare known for imparting stretchability to synthetic filaments. In onemethod, the fibers are two- or three-dimensionally crimped. In anothersuch method, stretchable filaments are produced from elastic polymers,for example, natural or synthetic rubber, or a synthetic elastomer, suchas polyurethane elastomer. However, there are drawbacks associated witheither of these methods. Ishii attempts to overcome the drawbacks ofsuch filaments by imparting asymmetry to filaments which are formed fromtwo polymers. Asymmetry causes the composite lobe filamentaryconstituents to be spirally coiled around the axial filamentaryconstituent in alternately reversed different directions. Thus, theresultant composite filament exhibits an improved stretchability and agood touch and gloss. However, due to their asymmetrical cross section,the Ishii fibers can develop, after mild heat treatment, substantialthree-dimensional or helical crimp in addition to their axial spiraltwist. This three-dimensional crimp characteristic imparts a torque tothe fibers and has been found to impart a substantial and oftenundesirable ‘edge curl’ to fabrics constructed of such fibers. Theinherent bulk and non-uniformity of such fibers also makes it difficultto construct uniform low basis weight or sheer fabrics from them. Forthese reasons the Ishii fibers are often unsatisfactory in fabricsknitted or woven from them.

[0007] U.S. Pat. No. 3,017,686 to Breen et al. also discloses a filamentmade from two polymers. These polymers are thermoplastic hard polymers,each having no elastomeric property. The polymers are chosen in order tohave a sufficient difference in shrinkage so that the fin of thefilament has a sinuous configuration, or “ruffle”. Breen is concernedwith the frequency by which the fins on a filament change direction sothat close packing between adjacent filaments is not possible, and isnot concerned with stretchability. Thus, the fiilaments disclosed inBreen do not exhibit the high recovery desired in many of today'sfabrics.

[0008] Thus, there is still a need for fibers and articles therefrom,that are stretchable and have excellent stretch and recovery power,preferably without undesired two- or three-dimensional crimpingcharacteristics, and for convenient methods of making such fibers andarticles.

SUMMARY OF THE INVENTION

[0009] The present invention solves the problems associated with theprior art by providing a stretchable synthetic polymer fiber having asubstantially radially symmetric cross-section. This imparts anunexpected combination of high stretch and high uniformity withoutsignificant levels of 2- or 3-dimensional crimp. As a result, the fibersof the invention are well-suited for use in smooth, non-bulky, highlystretchable fabrics. Such a finding was unexpected in view of theteaching to the contrary by U.S. Pat. No 4,861,660 to Ishii.

[0010] Thus, in accordance with the present invention, there is provideda stretchable synthetic polymer fiber having a substantially radiallysymmetric cross-section and comprising an axial core comprising athermoplastic elastomeric polymer and a plurality of wings comprising atleast one thermoplastic, non-elastomeric polymer attached to the core.

[0011] There is further provided in accordance with the invention agarment comprising the stretchable synthetic polymer fiber describedabove.

[0012] The invention further provides a melt spinning process forspinning continuous polymeric fibers comprising: passing a meltcomprising at least one thermoplastic non-elastomeric polymer and a meltcomprising a thermoplastic elastomeric polymer through a spinneret toform a plurality of stretchable synthetic polymeric fibers, each havinga substantially radially symmetric cross-section and comprising an axialcore comprising the elastomeric polymer and a plurality of wingscomprising the non-elastomeric polymer attached to the core; quenchingthe fibersafter they exit the capillary of the spinneret to cool thefibers, and collecting the fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a cross-sectional profile drawing of a six-wing fiber ofthe invention.

[0014]FIGS. 2A and 2B show fibers of the invention in which the spiraltwist is almost completely circumferential (2A) and in which the spiraltwist is almost completely noncircumferential (2B).

[0015]FIG. 3 shows a fiber of the invention in which the fiber isslightly wavy.

[0016]FIG. 4 is a representation of the cross-sectional shape of aparticular symmetrical two-wing fiber having a thin sheath around thecore and between the wings according to the invention.

[0017]FIG. 5 is a process schematic of an apparatus useful for makingfibers of this invention.

[0018]FIG. 6 is a representation of a stacked plate spinneret assembly,in side elevation, that can be used to make the fiber of the invention.

[0019]FIG. 6A is a representation of orifice plate A in plan view at 90°to the stacked plate spinneret assembly shown in FIG. 6, and takenacross lines 6A-6A of FIG. 6.

[0020]FIG. 6B is a representation of orifice plate B in plan view at 90°to the stacked plate spinneret assembly shown in FIG. 6, and takenacross lines 6B-6B of FIG. 6.

[0021]FIG. 6C is a representation of orifice plate C in plan view at 90°to the stacked plate spinneret assembly shown in FIG. 6, and takenacross lines 6C-6C of FIG. 6.

[0022]FIG. 7 is a representation of a stacked plate spinneret assembly,in side elevation, that can be used to make certain fibers according toanother embodiment of the present invention.

[0023]FIG. 7A is a representation of orifice plate A in plan view at 90°to the stacked plate spinneret assembly shown in FIG. 7, and takenacross lines 7A-7A of FIG. 7.

[0024]FIG. 7B is a representation of orifice plate B in plan view at 90°to the stacked plate spinneret assembly shown in FIG. 7, and takenacross lines 7B-7B of FIG. 7.

[0025]FIG. 7C is a representation of orifice plate C in plan view at 90°to the stacked plate spinneret assembly shown in FIG. 7, and takenacross lines 7C-7C of FIG. 7.

[0026]FIG. 7F is a representation of orifice plate F in plan view at 90°to the stacked plate spinneret assembly shown in FIG. 7, and takenacross lines 7F-7F of FIG. 7.

[0027]FIG. 7G is a representation of orifice plate G in plan view at 90°to the stacked plate spinneret assembly shown in FIG. 7, and takenacross lines 7G-7G of FIG. 7.

[0028]FIG. 7H is a representation of orifice plate H in plan view at 90°to the stacked plate spinneret assembly shown in FIG. 7, and takenacross lines 7H-7H of FIG. 7.

[0029]FIG. 8 is a cross-sectional profile drawing of a fiber of theinvention as exemplified in Example 7.

[0030]FIG. 9 is a cross-sectional profile drawing of a six-wing fiber ofthe invention as exemplifed in Example 7.

DETAILED DESCRIPTION OF THE INVENTION

[0031] In accordance with the present invention, there is provided astretchable synthetic polymer fiber, shown generally at 10 in FIGS. 1,2A, 2B, 3, 4, 8 and 9. The fiber of the present invention includes anaxial core, shown at 12 in FIG. 1, and a plurality of wings, shown at 14in FIG. 1. According to the present invention, the axial core comprisesa thermoplastic elastomeric polymer, and the wings comprise at least onethermoplastic, non-elastomeric polymer attached to the core. Preferably,the thermoplastic, non-elastomeric polymer is permanently drawable.

[0032] As used herein, the term “fiber” is interchangeable with the term“filament”. The term “yarn” includes yarns of a single filament. Theterm “multifilament yarn” generally relates to yarns of two or morefilaments. The term “thermoplastic” refers to a polymer which can berepeatedly melt-processed (for example melt-spun). By ‘elastomericpolymer’ is meant a polymer which in monocomponent fiber form, free ofdiluents, has a break elongation in excess of 100% and which whenstretched to twice its length, held for one minute, and then released,retracts to less than 1.5 times its original length within one minute ofbeing released. The elastomeric polymers in the fiber of the inventioncan have a flex modulus of less than about 14,000 pounds per square inch(96,500 kPascals), more typically less than about 8500 pounds per squareinch (58,600 kPascals) when present in a monocomponent fiber spunaccording to ASTM standard D790 Flexural Properties at RT or 23° C. andunder conditions substantially as described herein. As used herein,“non-elastomeric polymer” means any polymer which is not an elastomericpolymer. Such polymers can also be termed “low elasticity”, “hard: and“high modulus”. By “permanently drawable” is meant that the polymer hasa yield point, and if the polymer is stretched beyond such point it willnot return to its original length.

[0033] The fibers of the invention are termed “biconstituent” fiberswhen they are comprised of at least two polymers adhered to each otheralong the length of the fiber, each polymer being in a different genericclass, e.g., polyamide, polyester or polyolefin. If the elasticcharacteristics of the polymers are sufficiently different, polymers ofthe same generic class can be used, and the resulting fiber is a“bicomponent” fiber. Such bicomponent fibers are also within the scopeof the invention.

[0034] The fiber of the present invention is twisted around itslongitudinal axis, without significant two- or three-dimensionalcrimping characteristics. (In such higher-dimensional crimping, afiber's longitudinal axis itself assumes a zig-zag or helicalconfiguration; such fibers are not of the invention). The fiber of thepresent invention may be characterized as having substantially spiraltwist and one dimensional spiral twist. “Substantially spiral twist”includes both spiral twist that passes completely around the elastomericcore and also spiral twist that passes only partly around the core,since it has been observed that a fully 360° spiral twist is notnecessary to achieve the desirable stretch properties in the fiber. FIG.2A shows a fiber 10 with a substantially spiral twist which is almostcompletely circumferential, and FIG. 2B shows a fiber 10 with asubstantially spiral twist which is almost completelynoncircumferential. “One dimensional” spiral twist means that while thewings of the fiber can be substantially spiral, the axis of the fiber issubstantially straight even at low tension, in contrast to fibers having2- or 3-dimensional crimp. However, fibers having some waviness arewithin the scope of the invention, as illustrated by fiber 10 in FIG. 3.

[0035] The presence or absence of two- and three-dimensional crimp canbe gauged from the amount of stretch needed to substantially straightenthe fiber (by pulling out any non-linearities) and is a measure of theradial symmetry of fibers having spiral twist. The fiber of theinvention can require less than about 10% stretch, more typically lessthan about 7% stretch, for example about 4% to about 6%, tosubstantially straighten the fiber.

[0036] The fiber of the present invention has a substantially radiallysymmetric cross-section, as can be seen from FIG. 1. By “substantiallyradially symmetric cross-section” is meant a cross-section in which thewings are located and are of dimensions so that rotation of the fiberabout its longitudinal axis by 360/n degrees, in which “n” is an integerrepresenting the “n-fold” symmetry of the fibers, results insubstantially the same cross-section as before rotation. Thecross-section is substantially symmetrical in terms of size, polymer andangular spacing around the core. This substantially radially symmetriccross-section impartes an unexpected combination of high stretch andhigh uniformity without significant levels of two- or three-dimensionalcrimp. Such uniformity is advantageous in high-speed processing offibers, for example through guides and knitting needles, and in makingsmooth, non-‘picky’ fabrics, especially sheer fabrics like hosiery.Fibers which have a substantially radially symmetric cross-sectionpossess no self-crimping potential, i.e., they have no significant two-or three-dimensional crimping characteristics. See generally TextileResearch Journal, June 1967, p. 449.

[0037] For maximum cross-sectional radial symmetry, the core can have asubstantially circular or a regular polyhedral cross-section, e.g., asseen in FIGS. 1, 4, 8, and 9. By “substantially circular” it is meantthat the ratio of the lengths of two axes crossing each other at 90° inthe center of the fiber cross-section is no greater than about 1.2:1.The use of a substantially circular or regular polyhedron core, incontrast to the cores of U.S. Pat. No. 4,861,660, can protect theelastomer from contact with the rolls, guides, etc. as described laterwith reference to the number of wings. The plurality of wings can bearranged in any desired manner around the core, for example,discontinuously as depicted in FIG. 1, i.e., the wing polymer does notform a continous mantel on the core, or with adjacent wing(s) meeting atthe core surface, e.g., as illustrated in FIGS. 4 and 5 of U.S. Pat. No.3,418,200. The wings can be of the same or different sizes, provided asubstantially radial symmetry is preserved. Further, each wing can be ofa different polymer from the other wings, once again providedsubstantially radial geometric and polymer composition symmetry ismaintained. However, for simplicity of manufacture and ease of attainingradial symmetry, it is preferred that the wings be of approximately thesame dimensions, and be made of the same polymer or blend of polymers.It is also preferred that the wings discontinuously surround the corefor ease of manufacture.

[0038] While the fiber cross-section is substantially symmetrical interms of size, polymer, and angular spacing around the core, it isunderstood that small variations from perfect symmetry generally occurin any spinning process due to such factors as non-uniform quenching orimperfect polymer melt flow or imperfect spinning orifices. It is to beunderstood that such variations are permissible provided that they arenot of a sufficient extent to detract from the objects of the invention,such as providing fibers of desired stretch and recovery viaone-dimensional spiral twist, while minimizing two- andthree-dimensional crimping. That is, the fiber is not intentionally madeasymmetrical as in U.S. Pat. No. 4,861,660.

[0039] The wings protrude outward from the core to which they adhere andform a plurality of spirals at least part way around the core especiallyafter effective heating. The pitch of such spirals can increase when thefiber is stretched. The fiber of the invention has a plurality of wings,preferably 3-8, more preferably 5 or 6. The number of wings used candepend on other features of the fiber and the conditions under which itwill be made and used. For example, 5 or 6 wings can be used when amonofilament is being made, especially at higher draw ratios and fibertensions. In this case the wing spacing can be frequent enough aroundthe core that the elastomer is protected from contact with rolls,guides, and the like and therefore less subject to breaks, roll wrapsand wear than if fewer wings were used. The effect of higher draw ratiosand fiber tensions is to press the fiber harder against rolls andguides, thus splaying out the wings and bringing the elastomeric coreinto contact with the roll or guide; hence the preference for more thantwo wings at high draw ratios and fiber tensions. In monofilaments, fiveor six wings are often preferred for an optimum combination of ease ofmanufacture and reduced core contact. When a multifiber yarn is desired,as few as two or three wings can be used because the likelihood ofcontact between the elastomeric core and rolls or guides is reduced bythe presence of the other fibers.

[0040] While it is preferred that the wings discontinuously surround thecore for ease of manufacture, the core may include on its outsidesurface a sheath of a non-elastomeric polymer between points where thewings contact the core. FIG. 4 shows a fiber 10 having a sheath 16. Thesheath thickness can be in the range of about 0.5% to about 15% of thelargest radius of the fiber core. The sheath can help with adhesion ofthe wings to the core by providing more contact points between the coreand wing polymers, a particularly useful feature if the polymers in thebiconstituent fiber do not adhere well to each other. The sheath canalso reduce abrasive contact between the core and rolls, guides, and thelike, especially when the fiber has a low number of wings.

[0041] The core and/or wings of the multiwinged cross-section of thepresent invention may be solid or include hollows or voids. Typically,the core and wings are both solid. Moreover, the wings may have anyshape, such as ovals, T-, C-, or S-shapes (see, for example, FIG. 4).Examples of useful wing shapes are found in U.S. Pat. No. 4,385,886. T,C, or S shapes can help protect the elastomer core from contact withguides and rolls as described previously.

[0042] The weight ratio of total wing polymer to core polymer can bevaried to impart the desired mix of properties, e.g., desired elasticityfrom the core and other properties from the wing polymer. For example, aweight ratio of non-elastomeric wing polymer to elastomeric core polymerin the range of about 10/90 to about 70/30, preferably about 30/70 toabout 40/60, can be used. For high durability combined with high stretchin uses in which the fiber is not used with a companion yarn (forexample hosiery), a wing/core weight ratio in the range of about 35/65to about 50/50 is often preferred.

[0043] As noted above, the core of the fiber of the invention can beformed from any thermoplastic elastomeric polymer. Examples of usefulelastomers include thermoplastic polyurethanes, thermoplastic polyesterelastomers, thermoplastic polyolefins, thermoplastic polyesteramideelastomers and thermoplastic polyetheresteramide elastomers.

[0044] Useful thermoplastic polyurethane core elastomers include thoseprepared from a polymeric glycol, a diisocyanate, and at least one diolor diamine chain extender. Diol chain extenders are preferred becausethe polyurethanes made therewith have lower melting points than if adiamine chain extender were used. Polymeric glycols useful in thepreparation of the elastomeric polyurethanes include polyether glycols,polyester glycols, polycarbonate glycols and copolymers thereof.Examples of such glycols include poly(ethyleneether) glycol,poly(tetramethyleneether) glycol,poly(tetramethylene-co-2-methyl-tetramethyleneether) glycol,poly(ethylene-co-1,4-butylene adipate) glycol,poly(ethylene-co-1,2-propylene adipate) glycol,poly(hexamethylene-co-2,2-dimethyl-1,3-propylene adipate),poly(3-methyl-1,5-pentylene adipate) glycol, poly(3-methyl-1,5-pentylenenonanoate) glycol, poly(2,2-dimethyl-1,3-propylene dodecanoate) glycol,poly(pentane-1,5-carbonate) glycol, and poly(hexane-1,6-carbonate)glycol. Useful diisocyanates include1-isocyanato-4-[(4-isocyanatophenyl)methyl]benzene,1-isocyanato-2-[(4-isocyanato-phenyl)methyl]benzene, isophoronediisocyanate, 1,6-hexanediisocyanate,2,2-bis(4-isocyanatophenyl)propane,1,4-bis(p-isocyanato,alpha,alpha-dimethylbenzyl)benzene,1,1′-methylenebis(4-isocyanatocyclohexane), and 2,4-tolylenediisocyanate. Useful diol chain extenders include ethylene glycol, 1,3propane diol, 1,4-butanediol, 2,2-dimethyl-1,3-propylene diol,diethylene glycol, and mixtures thereof. Preferred polymeric glycols arepoly(tetramethyleneether) glycol,poly(tetramethylene-co-2-methyl-tetramethyleneether) glycol,poly(ethylene-co-1,4-butylene adipate) glycol, andpoly(2,2-dimethyl-1,3-propylene dodecanoate) glycol.1-Isocyanato-4-[(4-isocyanatophenyl)methyl]benzene is a preferreddiisocyanate. Preferred diol chain extenders are 1,3 propane diol and1,4-butanediol. Monofunctional chain terminators such as 1-butanol andthe like can be added to control the molecular weight of the polymer.Useful thermoplastic polyester elastomers include the polyetherestersmade by the reaction of a polyether glycol with a low-molecular weightdiol, for example, a molecular weight of less than about 250, and adicarboxylic acid or diester thereof, for example, terephthalic acid ordimethyl terephthalate. Useful polyether glycols includepoly(ethyleneether) glycol, poly(tetramethyleneether) glycol,poly(tetramethylene-co-2-methyltetramethyleneether) glycol [derived fromthe copolymerization of tetrahydrofuran and 3-methyltetrahydrofuran] andpoly(ethylene-co-tetramethyleneether) glycol. Useful low-molecularweight diols include ethylene glycol, 1,3 propane diol, 1,4-butanediol,2,2-dimethyl-1,3-propylene diol, and mixtures thereof; 1,3 propane dioland 1,4-butanediol are preferred. Useful dicarboxylic acids includeterephthalic acid, optionally with minor amounts of isophthalic acid,and diesters thereof (e.g., <20 mol %).

[0045] Useful thermoplastic polyesteramide elastomers that can be usedin making the core of the fibers of the invention include thosedescribed in U.S. Pat. No. 3,468,975. For example, such elastomers canbe prepared with polyester segments made by the reaction of ethyleneglycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol,2,2-dimethyl-1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol,1,10-decandiol, 1,4-di(methylol)cyclohexane, diethylene glycol, ortriethylene glycol with malonic acid, succinic acid, glutaric acid,adipic acid, 2-methyladipic acid, 3-methyladipic acid,3,4-dimethyladipic acid, pimelic acid, suberic acid, azelaic acid,sebacic acid, or dodecandioic acid, or esters thereof. Examples ofpolyamide segments in such polyesteramides include those prepared by thereaction of hexamethylene diamine or dodecamethylene diamine withterephthalic acid, oxalic acid, adipic acid, or sebacic acid, and by thering-opening polymerization of caprolactam.

[0046] Thermoplastic polyetheresteramide elastomers, such as thosedescribed in U.S. Pat. No. 4,230,838, can also be used to make the fibercore. Such elastomers can be prepared, for example, by preparing adicarboxylic acid-terminated polyamide prepolymer from a low molecularweight (for example, about 300 to about 15,000) polycaprolactam,polyoenantholactam, polydodecanolactam, polyundecanolactam,poly(11-aminoundecanoic acid), poly(12-aminododecanoic acid),poly(hexamethylene adipate), poly(hexamethylene azelate),poly(hexamethylene sebacate), poly(hexamethylene undecanoate),poly(hexamethylene dodecanoate), poly(nonamethylene adipate), or thelike and succinic acid, adipic acid, suberic acid, azelaic acid, sebacicacid, undecanedioic acid, terephthalic acid, dodecanedioic acid, or thelike. The prepolymer can then be reacted with an hydroxy-terminatedpolyether, for example poly(tetramethylene ether) glycol,poly(tetramethylene-co-2-methyltetramethylene ether) glycol,poly(propylene ether) glycol, poly(ethylene ether) glycol, or the like.

[0047] As noted above, the wings can be formed from any non-elastomeric,or hard, polymer. Examples of such polymers include non-elastomericpolyesters, polyamides, and polyolefins.

[0048] Useful thermoplastic non-elastomeric wing polyesters includepoly(ethylene terephthalate) (“2G-T”) and copolymers thereof,poly(trimethylene terephthalate) (“3G-T”), polybutylene terephthalate(“4G-T”), and poly(ethylene 2,6-naphthalate),poly(1,4-cyclohexylenedimethylene terephthalate), poly(lactide),poly(ethylene azelate), poly[ethylene-2,7-naphthalate], poly(glycolicacid), poly(ethylene succinate),poly(.alpha.,.alpha.-dimethylpropiolactone), poly(parahydroxybenzoate),poly(ethylene oxybenzoate), poly(ethylene isophthalate),poly(tetramethylene terephthalate, poly(hexamethylene terephthalate),poly(decamethylene terephthalate), poly(1,4-cyclohexane dimethyleneterephthalate) (trans), poly(ethylene 1,5-naphthalate), poly(ethylene2,6-naphthalate), poly(1,4-cyclohexylidene dimethyleneterephthalate)(cis), and poly(1,4-cyclohexylidene dimethyleneterephthalate)(trans).

[0049] Preferred non-elastomeric polyesters include poly(ethyleneterephthalate), poly(trimethylene terephthalate), and poly(1,4-butyleneterephthalate) and copolymers thereof. When a relatively high-meltingpolyesters such as poly(ethylene terephthalate) is used, a comonomer canbe incorporated into the polyester so that it can be spun at reducedtemperatures. Such comonomers can include linear, cyclic, and branchedaliphatic dicarboxylic acids having 4-12 carbon atoms (for examplepentanedioic acid); aromatic dicarboxylic acids other than terephthalicacid and having 8-12 carbon atoms (for example isophthalic acid);linear, cyclic, and branched aliphatic diols having 3-8 carbon atoms(for example 1,3-propane diol, 1,2-propanediol, 1,4-butanediol, and2,2-dimethyl-1,3-propanediol); and aliphatic and araliphatic etherglycols having 4-10 carbon atoms (for example hydroquinonebis(2-hydroxyethyl) ether). The comonomer can be present in thecopolyester at a level in the range of about 0.5 to 15 mole percent.Isophthalic acid, pentanedioic acid, hexanedioic acid, 1,3-propane diol,and 1,4-butanediol are preferred comonomers for poly(ethyleneterephthalate) because they are readily commercially available andinexpensive.

[0050] The wing polyester(s) can also contain minor amounts of othercomonomers, provided such comonomers do not have an adverse affect onfiber properties. Such other comonomers include5-sodium-sulfoisophthalate, for example, at a level in the range ofabout 0.2 to 5 mole percent. Very small amounts, for example, about 0.1wt % to about 0.5 wt % based on total ingredients, of trifunctionalcomonomers, for example trimellitic acid, can be incorporated forviscosity control.

[0051] Useful thermoplastic non-elastomeric wing polyamides includepoly(hexamethylene adipamide) (nylon 6,6); polycaprolactam (nylon 6);polyenanthamide (nylon 7); nylon 10; poly(12-dodecanolactam) (nylon 12);polytetramethyleneadipamide (nylon 4,6); polyhexamethylene sebacamide(nylon 6,10); poly(hexamethylene dodecanamide) (nylon 6,12); thepolyamide of dodecamethylenediamine and n-dodecanedioic acid (nylon12,12), PACM-12 polyamide derived from bis(4-aminocyclohexyl)methane anddodecanedioic acid, the copolyamide of 30% hexamethylene diammoniumisophthalate and 70% hexamethylene diammonium adipate, the copolyamideof up to 30% bis-(P-amidocyclohexyl)methylene, and terephthalic acid andcaprolactam, poly(4-aminobutyric acid) (nylon 4), poly(8-aminooctanoicacid) (nylon 8), poly(hapta-methylene pimelamide) (nylon 7,7),poly(octamethylene suberamide) (nylon 8,8), poly(nonamethyleneazelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9),poly(decamethylene sebacamide (nylon 10,10),poly[bis(4-amino-cyclohexyl)methane-1,10-decanedicarboxamide],poly(m-xylene adipamide), poly(p-xylene sebacamide),poly(2,2,2-trimethylhexamethylene pimelamide), poly(piperazinesebacamide), poly(11-amino-undecanoic acid) (nylon 11),polyhexamethylene isophthalamide, polyhexamethylene terephthalamide, andpoly(9-aminononanoic acid) (nylon 9) polycaproamide. Copolyamides canalso be used, for example poly(hexamethylene-co-2-methylpentamethyleneadipamide) in which the hexamethylene moiety can be present at about75-90 mol % of total diamine-derived moieties.

[0052] Useful polyolefins include polypropylene, polyethylene,polymethylpentane and copolymers and terpolymers of one or more ofethylene or propylene with other unsaturated monomers. For example,fibers comprising non-elastomeric polypropylene wings and an elastomericpolypropylene core are within the scope of the present invention; suchfibers are bicomponent fibers.

[0053] Combinations of elastomeric and non-elastomeric polymers caninclude a polyetheramide, for example, a polyetheresteramide, elastomercore with polyamide wings and a polyetherester elastomer core withpolyester wings. For example a wing polymer can comprise nylon 6-6, andcopolymers thereof, for example,poly(hexamethylene-co-2-methylpentamethylene adipamide) in which thehexamethylene moiety is present at about 80 mol % optionally mixed withabout 1% up to about 15% by weight of nylon-12, and a core polymer cancomprise an elastomeric segmented polyetheresteramide. “Segmentedpolyetheresteramide” means a polymer having soft segments (long-chainpolyether) covalently bound (by the ester groups) to hard segments(short-chain polyamides). Similar definitions correspond to segmentedpolyetherester, segmented polyurethane, and the like. The nylon 12 canimprove the wing adhesion to the core, especially when the core is basedon PEBAX™ 3533SN from Atofina. Another preferred wing polymer cancomprise a non-elastomeric polyester selected from the group ofpoly(ethylene terephthalate) and copolymers thereof, poly(trimethyleneterephthalate), and poly(tetramethylene terephthalate); an elastomericcore suitable for use therewith can comprise a polyetherester comprisingthe reaction product of a polyether glycol selected from the group ofpoly(tetramethyleneether) glycol andpoly(tetramethylene-co-2-methyltetramethyleneether) glycol withterephthalic acid or dimethyl terephthalate and a low molecular weightdiol selected from the group of 1,3-propane diol and 1,4-butane diol.

[0054] An elastomeric polyetherester core can also be used withnon-elastomeric polyamide wings, especially when an adhesion-promotingadditive is used, as described elsewhere herein. For example, the wingsof such a fiber can be selected from the group of (a) poly(hexamethyleneadipamide) and copolymers thereof with 2-methylpentamethylene diamineand (b) polycaprolactam, and the core of such a fiber can be selectedfrom the group of (a) polyetheresteramide and (b) the reaction productsof poly(tetramethyleneether) glycol orpoly(tetramethylene-co-2-methyltetramethyleneether) glycol withterphthalic acid or dimethyl terephthalate and a diol selected from thegroup of 1,3-propane diol and 1,4-butene diol.

[0055] Methods of making the polymers described above are known in theart and may include the use of catalysts, co-catalysts, andchain-branchers, as known in the art.

[0056] The high elasticity of the core permits it to absorbcompressional, torsional, and extensional forces as it is twisted by theattached wings when the fiber is stretched and relaxed. These forceswill cause delamination of the wing and core polymers if theirattachment is too weak. Bonding can be enhanced by selection of one ormore of the wing(s) and core compositions or by the use of a sheath asearlier described and/or the use of additives to either or both polymerswhich enhance bonding. Additives can be added to one or more of thewings, such that each wing has the same or different degrees ofattachment to the core. Thus, typically the core and wing polymersshould be selected such that they have a sufficient compatibility thatthey will bond to each other such that separation is minimized while thefibers are made and used.

[0057] Also, additives can be added to the wing and/or core polymers toimprove adhesion, for example, nylon 12, e.g., 5% by weight, based ontotal wing polymer, i.e., poly(12-dodecanolactam), also known as “12” or“N12”, commercially available as Rilsan “AMNO” from Atofina. Also,maleic anhydride derivatives (for example Bynel® CXA, a registeredtrademark of E. I. du Pont de Nemours and Company or Lotader®ethylene/acrylic ester/maleic anhydride terpolymers from Atofina) can beused to modify a polyether-amide elastomer to improve it adhesion to apolyamide. As another example, a thermoplastic novolac resin, forexample HRJ12700 (Schenectady International), having a number averagemolecular weight in the range of about 400 to about 5000, could be addedto an elastomeric (co)polyetherester core to improve its adhesion to(co)polyamide wings. The amount of novolac resin should be in the rangeof 1-20 wt %, with a more preferred range of 2-10 wt %. Examples of thenovolac resins useful herein include, but are not limited to,phenol-formaldehyde, resorcinol-formaldehyde,p-butylphenol-formaldehyde, p-ethylphenol-formaldehyde,p-hexylphenol-formaldehyde, p-propylphenol-formaldehyde,p-pentylphenol-formaldehyde, p-octylphenol-formaldehyde,p-heptylphenol-formaldehyde, p-nonylphenol-formaldehyde,bisphenol-A-formaldehyde, hydroxynapthaleneformaldehyde and alkyl- (suchas t-butyl-) phenol modified ester (such as penterythritol ester) ofrosin (particularly partially maleated rosin). See allowed U.S. patentapplication Ser. No. 09/384,605, filed Aug. 27, 1999 for examples oftechniques to provide improved adhesion between copolyester elastomersand polyamide.

[0058] Polyesters functionalized with maleic anhydride (“MA”) could alsobe used as adhesion-promoting additives. For, example, poly(butyleneterephthalate) (“PBT”) can be functionalized with MA by free radicalgrafting in a twin screw extruder, according to J. M. Bhaftacharya,Polymer International (August, 2000), 49: 8, pp. 860-866, who alsoreported that a few weight percent of the resulting PBT-g-MA was used asa compatibilizer for binary blends of poly(butylene terephthalate) withnylon 66 and poly(ethylene terephthalate) with nylon 66. For example,such an additive could be used to adhere more firmly (co)polyamide wingsto a (co)polyetherester core of the fiber of the present invention.

[0059] The polymers and resultant fibers, yarns, and articles used inthe present invention can comprise conventional additives, which can beadded during the polymerization process or to the formed polymer orarticle, and may contribute towards improving the polymer or fiberproperties. Examples of these additives include antistatics,antioxidants, antimicrobials, flameproofing agents, dyestuffs, lightstabilizers, polymerization catalysts and auxiliaries, adhesionpromoters, delustrants such as titanium dioxide, matting agents, andorganic phosphates.

[0060] Other additives that may be applied on the fibers, for example,during spinning and/or drawing processes include antistatics, slickeningagents, adhesion promoters, hydrophilic agents antioxidants,antimicrobials, flameproofing agents, lubricants, and combinationsthereof. Moreover, such additional additives may be added during varioussteps of the process as is known in the art.

[0061] The fibers of the invention can be in the form of continuousfilament (either a multifilament yarn or a monofilament) or staple(including for example tow or spun yarn). The drawn fibers of theinvention can have a denier per fiber of from about 1.5 to about 60(about 1.7-67 dtex). Fully drawn fibers of the invention with polyamidewing typically have tenacities of about 1.5 to 3.0 g/dtex, and fiberswith polyester wing, about 1-2.5 g/dtex, depending on wing/core ratios.The resulting fibers of the invention can have an after boil-off stretchof at least about 20%, preferably of at least about 40% for improvedcomfort and fit in the final garment.

[0062] While the above description focuses on advantages when the fiberhas a substantially radially symmetric cross-section, such symmetry,while often desired, is not required for embodiments of the inventionwhere:

[0063] (a) the stretchable synthetic polymer fiber has at least about20% after boil-off shrinkage and requires less than about 10% stretch tosubstantially straighten the fiber;

[0064] (b) the stretchable synthetic polymer fiber comprises an axialcore comprising an elastomeric polymer and a plurality of wingscomprising a non-elastomeric polymer attached to the core, wherein thecore includes on its outside surface a sheath of a non-elastomericpolymer between points where the wings contact the core;

[0065] (c) the stretchable synthetic polymer fiber comprises an axialcore comprising an elastomeric polymer and a plurality of wingscomprising a non-elastomeric polymer attached to the core, wherein thecore has a substantially circular or regular polyhedron cross section;or

[0066] (d) the stretchable synthetic polymer fiber comprises an axialcore comprising an elastomeric polymer and a plurality of wingscomprising a non-elastomeric polymer attached to the core, wherein atleast one of the wings has a T, C, or S shape.

[0067] Such fibers according to these four embodiments can be made andused and can provide one or more of the advantages described herein.

[0068] When a yarn comprising a plurality of fibers is made, the fiberscan be of any desired fiber count and any desired dpf, and the ratios ofthe elastomeric to non-elastomeric polymers can differ from fiber tofiber. The multifilament yarn can contain a plurality of differentfibers, for example, from 2 to 100 fibers. In addition, yarns comprisingthe fibers of the present invention can have a range of linear densitiesper fiber and can also comprise fibers not of the invention.

[0069] The synthetic polymer fibers of the present invention may be usedto form fabrics by known means including by weaving, warp knitting, weft(including circular) knitting, or hosiery knitting. Such fabrics haveexcellent stretch and power of recovery. The fibers can be useful intextiles and fabrics, such as in upholstery, and garments (includinglingerie and hosiery) to form all or a portion of the garment, includingnarrows. Apparel, such as hoisiery, and fabrics made using the fibersand yarns of the present invention have been found to be smooth,lightweight, and very uniform (“non-picky”) with good stretch andrecovery properties.

[0070] Further in accordance with the present invention, there isprovided a melt spinning process for spinning continuous polymer fibers.This process will be described with respect to FIG. 5, which is aschematic of an apparatus which can be used to make the fibers of thepresent invention. However, it should be understood that other apparatusmay be used. The process of the present invention comprises passing amelt comprising an elastomeric polymer through a spinneret to form aplurality of stretchable synthetic polymeric fibers including an axialcore comprising the elastomeric polymer and a plurality of wingsattached to the core and comprising the non-elastomeric polymer. Withreference to FIG. 5, a thermoplastic hard polymer supply, which is notshown, is introduced at 20 to a stacked plate spinneret assembly 35, anda thermoplastic elastomeric polymer supply, which is not shown, isintroduced at 22 to a stacked pflate spinneret assembly 35.Precoalescence or post coalescence spinneret packs can be used. The twopolymers can be extruded as undrawn filaments 40 from stacked platespinneret assembly 35 having orifices designed to give the desired crosssection. The process of the present invention further includes quenchingthe filaments after they exit the capillary of the spinneret to cool thefibers in any known manner, for example by cool air at 50 in FIG. 5. Anysuitable quenching method may be used, such as cross-flow air orradially flowing air.

[0071] The filaments are optionally treated with a finish, such assilicone oil optionally with magnesium stearate using any knowntechnique at a finish applicator 60 as shown in FIG. 5. These filamentsare then drawn, after quenching, so that they exhibit at least about 20%after boil-off stretch. The filaments may be drawn in at least onedrawing step, for example between a feed roll 80 (which can be operatedat 150 to 1000 meters/minute) and a draw roll 90 shown schematically inFIG. 5 to form a drawn filament 100. The drawing step can be coupledwith spinning to make a fully-drawn yarn or, if a partially orientedyarn is desired, in a split process in which there is a delay betweenspinning and drawing. Drawing can also be accomplished during windingthe filaments as a warp of yarns; called “draw warping” by those skilledin the art. Any desired draw ratio, (short of that which interferes withprocessing by breaking filament) can be imparted to the filament, forexample, a fully oriented yarn can be produced by a draw ratio of about3.0 to 4.5 times, and a partially oriented yarn produced by a draw ratioof about 1.2-3.0 times. Herein, draw ratio is the draw roll 90peripheral speed divided by the feed roll 80 peripheral speed. Drawingcan be carried out at about 15-100° C., typically about 15-40° C.

[0072] The drawn filament 100 optionally can be partly relaxed, forexample, with steam at 110 in FIG. 5. Any amount of heat-relaxation canbe carried out during spinning. The greater the relaxation, the moreelastic the filament, and the less shrinkage that occurs in downstreamoperations. The drawn, final filament, after being relaxed as describedbelow, can have at least about 20% after boil-off stretch. It ispreferred to heat-relax the just-spun filament by about 1-35% based onthe length of the drawn filaments before winding it up, so that it canbe handled as a typical hard yarn.

[0073] The quenched, drawn, and optionally relaxed filaments can then becollected by winding at a speed of 200 to about 3500 meters per minuteand up to 4000 meters per minute, at a winder 130 in FIG. 5. Or ifmultiple fibers have been spun and quenched, the fibers can beconverged, optionally interlaced, and then wound up for example at up to4000 meters per minute at winder 130, for example in the range of about200 to about 3500 meters per minute. Single filament or multifilamentyarns may be wound up at winder 130 in FIG. 5, in the same manner. Wheremultiple filaments have been spun and quenched, the filaments can beconverged and oprtionally interlaced prior to winding as is done in theart.

[0074] At any time after being drawn, the biconstituent filament may bedry- or wet-heattreated while fully relaxed to develop the desiredstretch and recovery properties. Such relaxation can be accomplishedduring filament production, for example during the above-describedrelaxation step, or after the filament has been incorporated into a yarnor a fabric, for example during scouring, dyeing, and the like.Heat-treatment in fiber or yarn form can be carried out using hot rollsor a hot chest or in a jet-screen bulking step, for example. It ispreferred that such relaxed heat-treatment be performed after the fiberis in a yarn or a fabric so that up to that time it can be processedlike a non-elastomeric fiber; however, if desired, it can beheat-treated and fully relaxed before being wound up as a high-stretchfiber. For greater uniformity in the final fabric, the fiber can beuniformly heat-treated and relaxed. The heat-treating/relaxationtemperature can be in the range of about 80° C. to about 120° C. whenthe heating medium is dry air, about 75° C. to about 100° C. when theheating medium is hot water, and about 101° C. to about 115° C. when theheating medium is superatmospheric pressure steam (for example in anautoclave). Lower temperatures can result in too little or noheat-treatment, and higher temperatures can melt the elastomeric corepolymer. The heat-treating/relaxation step can generally be accomplishedin a few seconds.

[0075] As noted above, the spinneret capillary has a designcorresponding to the desired cross-section of the fibers of the presentinvention, as described above, or to produce other biconstituent orbicomponent fibers. The capillaries or spinneret bore holes may be cutby any suitable method, such as by laser cutting, as described in U.S.Pat. No. 5,168,143, drilling, Electrical Discharge Machining (EDM), andpunching, as is known in the art. The capillary orifice can be cut usinga laser beam for good control of the cross-sectional symmetry of thefiber of the invention. The orifices of the spinneret capillary can haveany suitable dimensions and can be cut to be continuous(pre-coalescence) or non-continuous (post-coalescence). A non-continuouscapillary may be obtained by boring small holes in a pattern that wouldallow the polymer to coalesce below the spinneret face and form themulti-wing cross-section of the present invention.

[0076] For example, the filaments of the invention can be made with aprecoalescence spinneret pack as illustrated in FIGS. 6, 6A, 6B and 6C.In FIG. 6, a side elevation of the stacked plate spinneret assembly asshown in FIG. 5, the polymer flow is in the direction of arrow F. Thefirst plate in the spinneret assembly is plate D containing the polymermelt pool and is of a conventional design. Plate D rests upon meteringplate C (shown in cross sectional view FIG. 6C), which in turn restsupon optional distribution plate B (shown in cross sectional view FIG.6B), which rests on spinneret plate A (shown in cross sectional viewFIG. 6A), which is supported by spinneret assembly support plate E.Metering plate C is aligned and in contact with distribution plate Bbelow the metering plate, the distribution plate being above, alignedwith, and in contact with spinneret plate A having capillaries therethrough but lacking substantial counterbores, the spinneret plate(s)being aligned and in contact with a spinneret support plate (E) havingholes larger than the capillaries. The alignments are such that apolymer fed to the metering plate C can pass through distribution plateB, spinneret plate A and spinneret support plate E to form a fiber. Meltpool plate D, which is a conventional plate, is used to feed themetering plate. The polymer melt pool plate D and spinneret assemblysupport plate E are sufficiently thick and rigid that they can bepressed firmly toward each other, thus preventing polymer from leakingbetween the stacked plates of the spinneret assembly. Plates A, B, and Care sufficiently thin that the orifices can be cut with laser lightmethods. It is preferred that the holes in the spinneret support plate(E) be flared, for example at about 45°-60°, so that the just-spun fiberdoes not contact the edges of the holes. It is also preferred that, whenprecoalescence of the polymers is desired, the polymers be in contactwith each other (precoalescence) for less than about 0.30 cm, generallyless than 0.15 cm, before the fiber is formed so that thecross-sectional shape intended by the metering plate C, optionaldistribution plate D, and spinneret plate design E is more accuratelyexhibited in the fiber. More precise definition of the fibercross-section can also be aided by cutting the holes through the platesas described in U.S. Pat. No. 5,168,143, in which a multi-mode beam froma solid-state laser is reduced to a predominantly single-mode beam (forexample TM₀₀ mode) and focused to a spot of less than 100 microns indiameter and 0.2 to 0.3 mm above the sheet of metal. The resultingmolten metal is expelled from the lower surface of the metal sheet by apressurized fluid flowing coaxially with the laser beam. The distancefrom the top of the uppermost distribution plate to the spinneret facecan be reduced to less than about 0.30 cm.

[0077] To make filaments having any number of symmetrically placed wingpolymer portions, the same number of symmetrically arranged orifices areused in each of the plates. For example in FIG. 6A, spinneret plate A isshown in a plan view oriented 90° to the stacked plate spinneretassembly of FIG. 5. Plate A in FIG. 6A is comprised of six symmetricallyarranged wing spinneret orifices 140 connected to a central roundspinneret hole 142. Each of the wing orifices 140 can have differentwidths 144 and 146. Shown in FIG. 6B is the complementary distributionplate B having distribution orifices 150 tapering at an open end 152 tooptional slot 154 connecting the distribution orifices to central roundhole 156. Shown in FIG. 6C is metering plate C with metering capillaries160 for the wing polymer and a central metering capillary 162 for thecore polymer. Polymer melt pool plate D can be of any conventionaldesign in the art. Spinneret support plate E has a through hole largeenough and flared away (for example at 45-60°) from the path of thenewly spun filament so that the filament does not touch the sides of thehole, as is shown in FIGS. 5 and 6 side elevation. The stacked spinneretplate Assembly, plates A through D, are aligned so that core polymerflows from polymer melt pool plate D through central metering hole 162of metering plate C and through the 6 small capillaries 164, throughcentral circular capillary 156 of distribution plate B, through centralcircular capillary 142 of spinneret assembly plate A, and out throughlarge flared hole in spinneret support plate E. At the same time, wingpolymer flows from polymer melt pool plate D through wing polymermetering capillaries 160 of metering plate C, through distributionorifices 150 of distribution plate B (in which, if optional slot 154 ispresent, the two polymers first make contact with each other), throughwing polymer orifices 140 of spinneret plate A, and finally out throughthe hole in spinneret assembly support plate E.

[0078] The spinneret pack of the invention can be used for the meltextrusion of a plurality of synthetic polymers to produce a fiber. Inthe spinneret pack of the present invention, the polymers can be feddirectly into the spinneret capillaries, since the spinneret plate doesnot have a substantial counterbore. By no substantial counterbore ismeant that the length of any counterbore present (including any recessconnecting the entrances of a plurality of capillaries) is less thanabout 60%, and preferably less than about 40%, of the length of thespinneret capillary. Directly metering multicomponent polymer streamsinto specific points at the backside entrance of the fiber formingorifice in the spinneret plate eliminates problems in polymer migrationwhen multiple polymer streams are combined in feed channelssubstantially before the spinneret orifice, as is the norm.

[0079] It can be useful to combine the functions of two plates into onethrough the use of recessed grooves, on one or both sides of the singleplate with appropriate holes through the plate to connect the grooves.For example, recesses, grooves and depressions can be cut in theupstream side of the spinneret plate (for example by electrodischargemachining) and can function as distribution channels or shallow,insubstantial counterbores.

[0080] A variety of fibers comprising two or more polymers can be madewith the spinneret pack of the present invention. For example, otherbiconstituent fibers and bicomponent fibers not disclosed and/or claimedherein can be so made, including the cross-sections disclosed in U.S.Pat. Nos. 4,861,660, 3,458,390, and 3,671,379. The resulting fibercross-section can be for example side-by-side, eccentric sheath-core,concentric sheath-core, wing-and-core, wing-and-sheath-and core, and thelike. Moreover, the spinneret pack of the invention can be used to spinsplittable or non-splittable fibers.

[0081] In FIG. 7 a side elevation of the spinneret assembly stackedplates as shown in FIG. 5 is represented, where the polymer flow is inthe direction of the arrows. The use of this assembly is exemplied inExample 6 below. The first plate in the spinneret assembly is plate Dcontaining the polymer melt pool. This plate is of a conventional designknown in the art and contains passages 20 and 22 for introduction of thenon-elastomeric wing and sheath polymer and the elastomeric polymerrespectively. Plate D rests upon metering plate H, which in turn restsupon distribution plate G, which rests on spinneret plate F, which restsupon plate C, which rests upon plate B, which rests upon the spinneretor plate A, which is supported by spinneret assembly support plate E.The polymer melt pool plate D and spinneret assembly support plate E aresufficiently thick and rigid and pressed firmly toward each other, thuspreventing polymer from leaking between the stacked plates of thespinneret assembly. All other plates are sufficiently thin so that theorifices can be cut using laser light machining methods. FIGS. 7A-7C andFIGS. 7F-7H represent a plan view an alternative stacked plate spinneretassembly useful in making certain fibers of the present inventionrepresented by the cross sectional view in FIG. 5. The elastomeric corepolymer and non-elastomeric wing and sheath polymers are joined in FIGS.7A-7C and FIGS. 7F-7H using a precoalescence spinneret plate packassembly of the same general type illustrated in the side elevation viewof FIG. 6. In this alternative stacked plate spinneret assembly, aspinneret assembly support plate E, spinneret plate A, and polymer meltpool plate D are used, but five plates replace distribution plate B andmetering plate C. Through spinneret plate A, shown in FIG. 7A are cutwing orifices 210, a central core polymer and sheath polymer hole 214,and connecting slots 212. Plate B, as shown in FIG. 7B, is cut throughwith wing orifices 220 and a central core polymer and sheath polymerhole 222 centered above spinneret plate A. Centered above plate B isplate C, as shown in FIG. 7C, cut through it are cone-shaped wing andsheath polymer orifices 230, a central core polymer and sheath polymerhole 232. An annular shaped portion of the plate 234 remains connectedto the plate. Centered above plate C is plate F, shown in FIG. 7F, cutthrough with wing orifices 240 and central core polymer and sheathpolymer hole 242. Centered above plate F is plate G, as shown in FIG.7G, cut through with wing orifices 250, cone-shaped wing polymer andsheath polymer orifices 252, and a central core polymer hole 254.Centered above plate G is plate H, as shown in FIG. 7H, cut through itare wing polymer orifices 260, wing polymer and sheath polymer orifices262, and a central core polymer hole 264.

[0082] The invention is illustrated by the following non-limitingexamples. The following test methods were used in the Examples.

Test Methods

[0083] The term after boil-off stretch is used interchangeably in theart with the following terms: “% stretch”, “recoverable stretch”,“recoverable shrinkage” and “crimp potential”. The term “non-recoverableshrinkage” is used interchangeably with the following terms: “%shrinkage”, “apparent shrinkage” and “absolute shrinkage”.

[0084] Stretch properties (after boil-off stretch, after boil-offshrinkage and stretch recovery after boil-off) of the fibers prepared inthe Examples were determined as follows. A 5000 denier (5550 dtex) skeinwas wound on a 54 inch (137 cm) reel. Both sides of the looped skeinwere included in the total denier. Initial skein lengths with a 2 gramweight (length CB) and with a 1000 gram weight (0.2 gldenier) (lengthLB) were measured. The skein was subjected to 30 minutes in 95° C. water(“boil off”), and initial (after boil off) lengths with a 2 gram weight(length CA_(initial)) and with a 1000 gram weight (length LA_(initial))were measured. After measurement with the 1000 gram weight, additionallengths were measured with a 2 gram weight after 30 seconds (lengthCA_(30sec)) and after 2 hours (length CA_(2hrs)). Shrinkage afterboil-off was calculated as 100×(LB−LA)/LB. Percent after boil-offstretch was calculated as 100×(LA−CA@30 sec)/CA@30 sec. Stretch recoveryafter boil-off was calculated as 100×(LA−CA_(2hrs))/(LA−CA_(initial)).

[0085] The test for unload force at 20% and 35% available stretch wasperformed as follows. A biconstituent fiber skein having a total denierof 5000 (5550 dtex) after boil off was prepared. Both sides of thelooped skein were included in the total denier. An Instron tensiletester (Canton, Mass.) was used at 21° C. and 65% relative humidity. Theskein was placed in the tester jaws, between which there was a 3 inch(76 mm) gap. The tester was cycled through three stretch-and-relax(load-and-unload) cycles, each load cycle having a maximum of 500 gramsforce (0.2 grams per denier), and then the force on the 3^(rd) unloadcycle was determined. An effective denier (that is, the actual lineardensity at the test elongation) was determined for 20% and 35% availablestretch on the 3^(rd) unload cycle. “20% and 35% available stretch”means that the skein had been relaxed 20% and 35%, respectively, fromthe 500 gram force on the 3^(rd) cycle. The unload force at 20% and 35%available stretch was recorded in milligrams per effective denier(mg/denier).

[0086] Delamination of the wings from the core of a fiber was determinedby first winding a 5000 denier (5550 dtex) skein (the skein sizeincluded both sides of the resulting loop) on a 1.25 meter reel. Theskein was subjected to 102° C. steam in an autoclave for 30 minutes. A20 cm length individual fiber was selected from the skein and foldedonce in half. The open end of the resulting loop was taped together atthe bottom, and the taped loop was hung vertically on a hook. A weightof 1 gram per denier (50 grams for a 25 denier loop) was attached to thebottom (taped) end of the loop. The weight was raised to the point atwhich the loop was slack, and then lowered gently to stretch the loopand apply the full weight. After 10 such cycles the loop was examinedfor delamination under magnification and rated. Three samples were ratedas follows:

[0087] 0=No wing/core delamination visable along the fiber

[0088] 1=Slight delamination observed at one or more of the nodereversals

[0089] 2=Delamination observed where the fiber rubbed against the hookfrom which it was hanging

[0090] 3=Marginal delamination (in small loops, and only in a few spots)

[0091] 4=Small loops indicating delamination along the entire fiber

[0092] 5=Gross delamination (large loops all along the fiber)

[0093] The results from the three samples were averaged.

[0094] R₁ and R₂ were measured by superimposing two circles on aphotomicrograph of a cross-section of the fiber so that one circle (R₁)circumscribed the approximate outermost extent of the core polymer andthe other circle (R₂) inscribed the approximate innermost extent of thewing polymer.

EXAMPLE 1.A

[0095] A biconstituent fiber of the invention having a symmetricalsix-wing cross-section substantially as shown in FIG. 1 was spun usingan apparatus as illustrated in FIG. 5. A single fiber 40 was spun usingspinneret plate 35 and a spinneret temperature of 265° C. At 20 in FIG.5 a melted nylon polymer conventionally prepared and having a relativeviscosity of about 45-60, was introduced to the spin pack assembly 30.The nylon polymer which formed the wing portion of the biconstituentfilament was poly(hexamethylene-co-2-methylpentamethylene adipamide) inwhich the hexamethylene moiety was present at 80 mol % (6/MPMD(80/20)-6)to which 5% by weight based on total wing polymer, nylon 12(poly(12-dodecanolactam)) (also known as “12” or “N12”) (Rilsan® “AMNO”from Atofina) had been added. The nylon 12 was added to aid wing-to-corecohesion. The wing portions were 45 wt % of the fiber. A second polymer,which formed the core of the fiber, was introduced at 22 to spin packassembly 30 in FIG. 5. The core polymer was an elastomeric segmentedpolyetheresteramide (PEBAX™ 3533SN from Atofina; flex modulus 2800 psi(19,300 kPascals)) and was metered volumetrically to create a core whichwas 55 wt % of the biconstituent fiber.

[0096] Precoalescence spinneret pack assembly 30 was comprised ofstacked plates labeled A through E in FIG. 6. Orifices were cut through0.015 inch (0.038 cm) thick stainless steel spinneret plate A as sixwings arranged symmetrically at 60 degrees, around a center of symmetryusing a process as described in U.S. Pat. No. 5,168,143. As illustratedin FIG. 6A, each wing orifice 140 was straight with a long axiscenterline passing through the center of symmetry and had a length of0.049 inches (0.124 cm) from tip to the circumference of a central roundspinneret hole 142 (diameter 0.012 inches [0.030 cm]) with origin ofradius the same as the center of symmetry. There was no counterbore atthe entrance to the spinneret capillary. The wing length 144 from tip to0.027 inches (0.069 cm) was 0.0042 inches (0.0107 cm) wide; theremaining length 146 of 0.022 inches (0.056 cm) was 0.0032 inches(0.0081 cm) wide. The tip of each wing was radius-cut at one-half thewidth of the tip. Distribution plate B of 0.015 inches (0.038 cm)thickness was aligned with the spinneret plate A so that itsdistribution orifices were congruent with the spinneret orifices in thespinneret plate A. The six wing orifices of plate B were 0.094 inch(0.239 cm) long and 0.020 inch (0.051 cm) wide, and their wing tips wererounded to a radius one-half their width. As illustrated in FIG. 6B,each of the six wing orifices 150 of distribution plate B tapered to arounded (0.006 inch [0.015 cm] diameter) open end 156 and then continuedas a slot of 0.013 inch (0.033 cm) length and 0.0018 inch (0.0046 cm)length to central hole 156. The central hole 156 in this plate was0.0125 inches (0.032 cm) in diameter. A slot 154 connected the centralhole with the end of each wing distribution orifice. Metering plate Cwas of 0.010 inch (0.025 cm) thickness (see FIG. 6C). Each of themetering holes was centered above a wing long axis centerline or abovethe center of symmetry in distribution plate B. The central meteringhole 152 and one hole per wing 160 were 0.010 inch (0.025 cm) diameter;the centers of holes 160 were 0.120 inch (0.305 cm) from the center ofhole 162. The central metering hole was fed filtered melted elastomericpolymer from a conventional melt pool plate D (see FIG. 6) and formedthe core element within the final fiber. The outer six metering holes ofplate C were fed a non-elastomeric polymer from melt pool plate D tobecome the polymer wings. Large holes (typically 0.1875 inches (0.4763cm) in diameter) in spinneret support plate E (see again FIG. 6) werealigned with the spinneret orifices in spinneret plate A and were flaredat 45°. Spinneret plate A, distribution plate B, and metering plate Cwere sandwiched by melt pool plate D and spinneret support plate E.Typically, plate E was 0.2-0.5 inches (0.4-1.3 cm) thick, and plate Dwas 0.02-0.03 inches (0.05-0.08 cm) thick.

[0097] A single freshly spun fiber 40 (see FIG. 5) was cooled tosolidify it by a flow of air 50, and a finish (about 5 wt % based onfiber) comprising silicone oil and a metal stearate was applied at 60.The fiber was forwarded to a draw zone between feed roll 80 and drawroll 90, taking several wraps about each roll. The speed of draw roll 90was four times that of feed roll 80 for a draw ratio of 4×; the latterspeed was 350 meters per minute. The fiber was then treated with steamat 6 pounds per square inch 0.87 kilopascal) in a chamber 110; winder130 was operated at a speed 20% lower than that of draw roll 90 so thatthe fiber was partly (20%) relaxed in order to reduce shrinkage in thefinal fiber. The drawn and partly relaxed fiber 120 was wound up atwinder 130 and had a linear density of 27 denier (30 dtex).

EXAMPLE 1.B

[0098] A biconstituent yarn of the invention having 10 fibers, each with6 radially symmetric wings of nylon 6-12 (poly(hexamethylenedodecanamide)), (intrinsic viscosity 1.18), Zytel® 158, a registeredtrademark of E. I. du Pont de Nemours and Company; flex modulus 295,000psi (2.0 million kPascals) and a core of PEBAX™ 3533SA was spun usingthe apparatus of FIG. 5 in substantially the same way as in Example 1.A,except that the spinneret temperature was 240° C., distribution plate Bhad no slot 154, and 4 wt % of a polyetherester-based finish was appliedin place of the finish applied in Example 1.A, the draw ratio was 3.75×,and the yarn was relaxed 15%. The drawn and partly relaxed yarn had alinear density of 80 denier (88 dtex). A photomicrograph of thecross-section of the resulting fiber is shown in FIG. 8.

EXAMPLE 1.C

[0099] A biconstituent yarn of the invention of 10 filaments with fiveradially symmetric wings on each filament of poly(butyleneterephthalate) (4G-T) (Crastin® Type 6129, a registered trademark of E.I. du Pont de Nemours and Company; 350,000 psi flex modulus (2.4 millionkPascals)) and having a HYTREL® (a registered trademark of E. I. du Pontde Nemours & Company, Inc.) 3078 elastomeric polyetherester core wasprepared analogously to that of Example 1.A except that: each plate hadfive holes for wing polymer supply arranged symmetrically at 72° apart;the metering plate C had an additional set of holes, one per wing on thecenterline of the wing; the 4G-T wings had no cohesion additive; 4 wt %of a finish comprising polysiloxane as described in U.S. Pat. No.4,999,120 was used in place of the finish applied in Example 1.A; thefeed roll speed was 250 meters per minute; the draw ratio was 3.6×; andthe steam pressure for relaxation was 20 pounds per square inch 2.9kilopascal). The drawn and partly relaxed yarn had a linear density of150 denier (165 dtex).

[0100] With regard to the additional set of holes on the metering plateC, one per wing on the centerline of the wing, each hole was 0.005inches (0.013 cm) in diameter and 0.0475 inches (0.121 cm) from thecenter of symmetry of the holes. However, the additional holes were notfed melted polymer by melt pool plate D.

[0101] The yarns prepared in Example 1.A-C were compared for afterboil-off stretch, after boil-off shrinkage, and stretch recovery afterboil-off. The test was carried out by first preparing a 5000 denier(5550 dtex) skein of yarn which was wound on a 54 inch (137 cm) reel.Both sides of the looped skein were included in the total denier. Theinitial skein length with a light and a heavy weight were measured andthe following measurements were recorded:

[0102] CB=measured skein length with 2 gram weight

[0103] LB=measured skein length with 1000 gram weight (0.2 grams perdenier).

[0104] The following initial and final lengths were measured after hotaqueous treatment or “boil off” which subjected the skein to a 30 minutedip in 95° C. water:

[0105] CA (initial)=measured skein length after treatment with 2 gramweight

[0106] LA=measured skein length after treatment with 1000 gram weightapplied (0.2 grams per denier)

[0107] CA (30 seconds)=measured skein length 30 seconds after LAmeasured with 1000 gram weight removed and 2 gram weight applied

[0108] CA (2 hrs)=measured skein length 2 hours after LA measured, with2 gram weight applied

[0109] These measurements were used to calculate the yarncharacteristics as follows:

[0110] Percent Stretch after boil off=100×(LA−CA@30sec)/CA@30sec

[0111] Boil-Off Shrinkage=100×(LB−LA)/LB.

[0112] Percent Recovery after boil-off=100×(LA−CA@2hrs) (LA−CA@initial)

[0113] The yarn properties of boil-off shrinkage, percent after boil-offstretch and stretch recovery reported in Table 1 for the yarns ofExample 1.A-1.C are suitable for hosiery and apparel applications. TABLE1 Example 1.A Example 1.B Example 1.C Drawn 27 den. 80 den. 150 den.denier/no. of (30 dtex)/1 (88dtex)/10 (165dtex.)/10 fibers Number of  6 6  5 Wings Wing 6/MPMD-6 + 6-12 4G-T 5% N12 Core PEBAX ™ PEBAX ™HYTREL ™ 3533SN 3533SA 3078 % stretch after 78 76 75 boil off % Boil-Off19 16 17 Shrinkage % recovery 94 92 94 after boil off

EXAMPLE 2

[0114] A sheer hosiery leg blank was knitted using four fibers preparedin Example 1.A. A commercial four-feed hosiery machine (Lanoti Model400, 402 needles) was used. The fibers were knit in a typical four-feed,every-course jersey leg construction typical for commercial pantyhose.

[0115] The filaments were knit directly from the wound package andbehaved like a “hard” yarn, that is, without elastomeric character. Thefour filaments were independently fed to the machine needles directlythrough standard creel guides, each of which had a conventional dancerring tensioner typically used for feeding non-elastomeric yarns tohosiery knitting machines. The hose blanks were knit at 700 rpm in thethigh area and 800 rpm in the ankle. Each blank was knit in about 2minutes, including a panty portion in a standard nylon spandex pantystyle.

[0116] The griege size of the hose blank was adjusted by conventionalmeans to meet standard size specifications. Next, the greige hosiery legblanks were heat-treated to activate the latent stretch characteristicin the biconstituent fiber. This was done in one of two ways. In onemethod, the greige pantyhose blanks were placed in a cloth bag andagitated in a water bath at room temperature. The bath was raised intemperature with steam to 85° C. over 45 mintues and then cooled withroom temperature water while agitated. The bagged blanks were dewateredin a centrifuge and dried in an oven at 100° C. In another method, theblanks were shrunk by tumble steaming using atmospheric pressure steamfor 30 minutes. In either case, the fiber of the invention was madehighly stretchable but not bulky by the relaxed hot treatment. Theblanks were then removed from the bags and sewn into pantyhose in aconventional way. The garments were then rebagged and dyed usingstandard acid dye procedures for nylon hosiery with a maximum dye bathtemperature of 99° C. The dyed garments were dewatered, dried, andboarded on standard 4 inch (10.2 cm) base width hosiery boards. Theboarding autoclave was set to treat the hose for 4 seconds at 102° C.,followed by drying at 99° C. for 30 seconds. The pantyhose were placedon the boards so that they remained as small as possible while holdingthe fabric in a wrinkle-free state. The appearance of the finishedgarments was suitable for sheer hosiery applications, and they showedgood stretch and recovery. Their shrinkage at each stage of finishingwas measured as described below, and the magnitude and consistency ofsizing of the finished goods was found suitable for the commercialmanufacture of hosiery products.

[0117] Cross-stretch measurements were taken on the greige fabric andagain after a ten-minute hot aqueous treatment (boil off) to assessshrinkage and potential to meet typical size standards. Thecross-stretch measurements were made by slipping each blank over thejaws of a Dinema S.R.L. instrument, separating the jaws, and measuringthe percent stretch when the force on the jaws reached 4500 grams.Measurements were taken 3 inches (7.6 cm) below the crotch (“Thigh”), ½way between the toe and the crotch (“Knee”), and about 3.5 inches (8.9cm) up from the toe (“Foot”). The leg pull stretch was measuredsimilarly except that each blank was clamped length-wise between thejaws of the instrument. The stretch values were 22% for the thigh, 21%for the knee, 17% for the foot, and 138% for the leg pull. A shrinkagelevel of approximately 17-24% from greige to boil-off dimension wasdetermined for the thigh, knee, foot, and leg pull and was littlechanged after further boarding and dyeing, indicating that the blankswere dimensionally stable, as needed for commercial use.

EXAMPLE 3

[0118] Yarns from Example 1.B were used to construct a weft-stretchwoven fabric on a shuttle loom in a “Crowfoot” construction with TACTEL®a registered trademark of E. I. du Pont de Nemours and Company) 70denier (78 decitex) 6-6 nylon in the warp with 102 ends per inch(40/cm). The Example 1.B 80 denier (89 decitex) 10 filamentbiconstituent yarn was the weft fiber at 100 picks per inch (39/cm). Thegreige woven fabric width was 62.5 inches (159 cm). This fabric wasfinished using a relaxed state scour at 71° C., followed by a secondrelaxed scour at 118° C. After drying, this fabric had a relaxed widthof 36 inches (91 cm). This fabric was dyed at 100° C. with standard aciddyes for nylon. The after dyeing wet width was 33 inches (84 cm).Finally, this fabric was air dried without heat setting. The final widthwas 33.25 inches (84 cm). This fabric was non-bulky, smooth andnon-wrinkled after only air drying. The fabric showed good stretch andrecovery, and excellent hard fiber hand and aesthetics. In the relaxedfinished state, this fabric had the following properties: Basis weight:4.45 oz./yard² (151 grams/m²); Thickness: 0.0103 inch (0.0262 cm); FillCount: 112 weft threads per inch (44/cm); Warp Count: 192 warp threadsper inch (76.8/cm).

[0119] A 5 cm width by 10 cm length of this fabric was evaluated forhand stretch to full extension in the weft. The fabric could bestretched 65% of its relaxed length and showed recovery after handstretching of greater than 95% of the difference between its stretchedand relaxed length.

EXAMPLE 4

[0120] Yarns from Example 1.C were used to construct a weft-stretchwoven fabric on a shuttle loom in a plain weave construction with DuPontTACTEL® 70 denier (78 decitex) 6-6 nylon in the warp with 102 ends perinch (40/cm). The Example 1.C 150 denier (166 decitex) 10 filamentbiconstituent yarn was the weft fiber at 50 picks per inch (19.7/cm).The greige woven fabric width was 63.5 inches (161 cm). This fabric wasfinished using a relaxed state scour at 82° C. for 20 minutes. Thefabric was dyed at 100° C. for 60 minutes with standard acid dyes fornylon, and dried at 93° C. The final dry width was 33.5 inches (85 cm).This fabric was non-bulky, smooth and non-wrinkled. The fabric showedgood stretch and recovery, and excellent hard fiber hand and aesthetics.In the relaxed finished state, this fabric had the following properties:Basis weight: 4.5 oz./yard² (152 grams/m²); Thickness: 0.0115 inch(0.0292 cm); Fill Count: 60 weft threads per inch (23.6/cm); Warp Count:204 warp threads per inch (80/cm).

[0121] A 5 cm width by 10 cm length of this fabric was evaluated forhand stretch to full extension in the weft. The fabric could bestretched 72.8% of its relaxed length and showed recovery after handstretching of greater than 97% of the difference between its stretchedand relaxed length.

EXAMPLE 5

[0122] This example illustrates the benefit of using an adhesionpromoter (see Example 5B) in making the fiber of the invention.Biconstituent fibers were spun using the apparatus illustrated in FIG. 5and the conditions and spinneret pack analogous to those described forExample 1.A. Each drawn fiber had a linear density of 26 denier (28.6dtex). After-boil-off properties and delamination ratings are reportedin Table 2.

EXAMPLE 5.A.

[0123] The elastomeric core polymer was an elastomericpolyetheresteramide (PEBAX™ 3533SN, from Atofina) and was meteredvolumetrically during spinning to create a core which was 51 wt % ofeach fiber. The nylon blend, which formed the six wings, waspoly(hexamethylene-co-2-methylpentamethylene adipamide), as described inExample 1.A. A photomicrograph of the cross-section of the resultingfiber is shown in FIG. 9.

EXAMPLE 5.B.

[0124] A fiber having 6 wings of 6/MPMD(80/20)-6 polyamide(poly(hexamethylene-co-2-methylpentamethylene adipamide) in which thehexamethylene moiety was present at 80 mol %) and a core of elastomericpolyetheresteramide (PEBAX™ 3533SN) was spun substantially as in Example5.A. except that 5 wt % poly(12-dodecanolactam as described in Example1.A was added to the wing polymer to aid in wing-to-core cohesion.

[0125] Delamination of the wings from the core of a fiber was determinedby first winding a 5000 denier (5550 dtex) skein (the skein sizeincluded both sides of the resulting loop) on a 1.25 meter reel. Theskein was subjected to 102° C. steam in an autoclave for 30 minutes. Anindividual fiber having a length of 20 cm was selected from the skeinand folded once in half. The open end of the resulting loop was tapedtogether at the bottom, and the taped loop was hung vertically on ahook. A weight of 1 gram per denier (0.9 dN/tex) (50 grams for a 25denier [28 dtex] loop) was attached to the bottom (taped) end of theloop. The weight was raised to the point at which the loop was slack,and then lowered gently to stretch the loop and apply the full weight.After 10 such cycles the loop was examined for delamination undermagnification and rated. Three samples were rated as follows:

[0126] 0=No wing/core delamination visable along the fiber

[0127] 1=Slight delamination observed at one or more of the nodereversals

[0128] 2=Delamination observed where the fiber rubbed against the hookfrom which it was hanging

[0129] 3=Marginal delamination (in small loops, and only in a few spots)

[0130] 4=Small loops indicating delamination along the entire fiber

[0131] 5=Gross delamination (large loops all along the fiber)

[0132] The results from the three samples were averaged and are reportedin Table 2. TABLE 2 Example Example 5.A 5.B Wing polymer 6/MPMD-66/MPMD-6 + 5% N12 Core polymer PEBAX ™ PEBAX ™ 3533SN 3533SN % stretch66.7 92.1 after boil off % shrinkage 31 19 after boil off Delamination3.8 1.2 rating

[0133] The results show that using selected pairs of core and wingpolymers can give a fiber that resists delamination (Example 5.A) andthat using an adhesion promoter can have a beneficial effect on furtherreducing the delamination rating of the fiber, for example to below arating of about 2.5 (Example 5.B).

EXAMPLE 6

[0134] This example illustrates a fiber of the invention having aparticular two-wing cross-section and the use of a thin sheathcomprising the same polymer as the wings and continuously connecting thewings. In this case a side of each wing (as distinct from an end of thewing) is attached to the core so the wing has a T-shape (See FIG. 4).The thin sheath encapsulates the core and eliminates the contact of theelastomer with surfaces.

[0135] In making the fiber in this Example, poly(hexamethylenedodecanamide) (Zytel® 158) was used as the wing polymer and apolyetherester having a poly(tetramethylene-co-2-methyltetramethyleneether) glycol soft segment and butylene terephthalate (4G-T) hardsegment, prepared substantially as described in U.S. Pat. No. 4,906,721was used as the core. The amount of 3-methyltetrahydrofuran incorporatedinto the copolyether glycol was 9 mol %, the glycol number average MWwas 2750, and the mole ratio of 4G-T to copolyether glycol was 4.6:1.

[0136] The polymers were spun using the configuration of spinneretplates as shown in FIGS. 7A-7C and FIGS. 7F-7H. In spinneret plate A(FIG. 7A), the sheath-core hole had a diameter of 0.011 inches [0.028cm]. The core-and-sheath hole of first plate B (FIG. 7B) had a diameterof 0.008 inches [0.020 cm]. The core-and-sheath hole of first plate B(FIG. 7B) had a diameter of 0.025 inches [0.064 cm], and the annulus ofthis plate had an outer diameter of 0.100 inches [0.254cm]. Thecore-and-sheath hole of third plate F (FIG. 7F) had a diameter of 0.125inches [0.318 cm]. The central core hole of fourth plate G (FIG. 7G) hada diameter 0.025 inches [0.064 cm]) and the annulus of this plate had anouter diameter of 0.100 inches [0.254 cm]. The central core hole of thefifth plate H (FIG. 7H) had a diameter of 0.033 inches [0.084 cm].

[0137] The central holes and annuli were of dimensions such that thepolymer flows were as follows. Core polymer was fed straight through thecentral core holes of each of the plates. Wing-and-sheath polymer wasfed to the wing orifices and outer part of the core hole of spinneretplate A by the wing orifices and the outer part of central hole of plateB, respectively. The first contact between wing and core was thereforein spinneret plate A. The cone-shaped wing-and-sheath orifices of plateC fed part of the polymer downward into the wing orifices of plate B andfed part of the polymer upward to the outer edge of central hole ofplate F, thus forming part of the sheath. The cone-shapedwing-and-sheath orifices of plate C were fed by the orifices of plate F.The orifices of plate F were fed by the orifices of plate G. Thecone-shaped orifice of plate G fed the outer edge of the central hole ofplate F, thus forming the other part of the sheath. The first contactbetween sheath and core was therefore at plate F. The orifices in plateH fed the orifices, respectively, in plate G.

[0138] In the fibers made in this example, the weight ratio of wing tocore was 56/44, and the sheath was about 10 wt % of the total wingcontent. This percent can be varied from about 2 to about 20 wt %. Tenfilaments were spun, drawn 3.6× without relaxation, and wound up at 900meters per minute. Upon relaxed exposure to atmospheric pressure steam,the fiber immediately shrank and thereafter exhibited good stretch andrecovery.

EXAMPLE 7

[0139] This example shows that fully circumferential spiral twist isunnecessary to achieve the stretch and recovery desired in the fiber ofthe invention.

[0140] The wing and core polymers used in Example 1.C were spun througha spinneret pack similar to that used in Example 1.A, with the followingdifferences: the wing orifices in spinneret plate A had a length of0.023 inches (0.058 cm), and the central round hole had a diameter of0.008 inches (0.200 cm); distribution plate B lacked slots 154 (see FIG.6B); ten fibers were spun to form a yarn, each fiber being 33 wt % wingpolymer; the yarn was drawn 3.3× without relaxation and wound up at 1040meters/minute. FIGS. 8 and 9 are photomicrographs of the resultingfibers in the yarn, showing both circumferential spiral twist andnoncircumferential spiral twist of the wings. Circumferential twistsections and noncircumferential twist sections had similar responses tofull relaxation: a 10 cm length subjected to atmospheric pressure steamshrank to 4.8 cm. Repeated stretch-and-relax cycles (to 10 cm) resultedin a length of 6.5 cm, which however again shrank to 4.8 cm on renewedexposure to atmospheric pressure steam, indicating a reversible set.

[0141] While the invention has been described in conjunction with thedetailed description thereof, it is to be understood that the foregoingdescription is exemplary and explanatory in nature, and is intended toillustrate the invention and its preferred embodiments. Through routineexperimentation, the artisan will recognize apparent modifications andvariations that may be made without departing from the spirit of theinvention.

What is claimed is:
 1. A stretchable synthetic polymer fiber having asubstantially radially symmetric cross-section and comprising an axialcore comprising a thermoplastic, elastomeric polymer, and a plurality ofwings comprising at least one thermoplastic, non-elastomeric polymerattached to the core.
 2. The fiber of claim 1, which comprises from 3 to8 wings, has an after-boil-off stretch of at least about 20%, requiresless than about 10% stretch to substantially straighten the fiber, has asubstantially circular core cross-section, and wherein the weight ratioof non-elastomeric wing polymer to elastomeric core polymer is in therange of about 10/90 to about 70/30.
 3. The fiber of claim 1, whereinthe non-elastomeric polymer is selected from the group consisting ofnon-elastomeric polyamides, polyolefins and polyesters, and theelastomeric polymer is selected from the group consisting ofthermoplastic polyurethanes, thermoplastic polyester elastomers,thermoplastic polyolefins, thermoplastic polyesteramide elastomers andthermoplastic polyetheresteramide elastomers.
 4. The fiber of claim 1,wherein the non-elastomeric polymer is selected from the groupconsisting of a) poly(hexamethylene adipamide) and copolymers thereofwith 2-methylpentamethylene diamine and b) polycaprolactam, and theelastomeric polymer is a polyetheramide.
 5. The fiber of claim 1,wherein the non-elastomeric polymer is selected from the groupconsisting of poly(ethylene terephthalate) and copolymers thereof,poly(trimethylene terephthalate), and poly(tetramethyleneterephthalate), and the elastomeric polymer is selected from the groupconsisting of the reaction products of poly(tetramethyleneether) glycolor poly(tetramethylene-co-2-methyltetramethyleneether) glycol withterephthalic acid or dimethyl terephthalate and a diol selected from thegroup consisting of 1,3-propane diol and 1,4-butane diol.
 6. The fiberof claim 1, wherein the core includes on its outside surface a sheath ofa non-elastomeric polymer between points where the wings contact thecore.
 7. The fiber of claim 1 further comprising an additive added tothe non-elastomeric polymer of the wings to improve adhesion of thewings to the core, wherein this fiber has a delamination rating belowabout 2.5.
 8. The fiber of claim 7, wherein the non-elastomeric polymeris selected from the group consisting of (a) poly(hexamethyleneadipamide) and copolymers thereof with 2-methylpentamethylene diamineand (b) polycaprolactam, and the elastomeric polymer is apolyetheresteramide.
 9. A stretchable synthetic polymer fiber having atleast about 35% after boil-off shrinkage and which requires less thanabout 10% stretch to substantially straighten the fiber.
 10. Astretchable synthetic polymer fiber comprising an axial core comprisingan elastomeric polymer and a plurality of wings comprising anon-elastomeric polymer attached to the core, wherein the core includeson its outside surface a sheath of a non-elastomeric polymer betweenpoints where the wings contact the core.
 11. A stretchable syntheticpolymer fiber comprising an axial core comprising an elastomeric polymerand a plurality of wings comprising a non-elastomeric polymer attachedto the core, wherein the core has a substantially circular or regularpolyhedron cross section.
 12. A stretchable synthetic polymer fibercomprising an axial core comprising an elastomeric polymer and aplurality of wings comprising a non-elastomeric polymer attached to thecore, wherein at least one of the wings has a T, C, or S shape.
 13. Agarment comprising the fiber of claims 1, 9, 10, 11 or
 12. 14. A meltspinning process for spinning continuous polymeric fibers comprising:passing a melt comprising at least one thermoplastic non-elastomericpolymer and a melt comprising a thermoplastic elastomeric polymerthrough a spinneret to form a plurality of stretchable syntheticpolymeric fibers having a substantially radially symmetric cross-sectionand comprising an axial core comprising the elastomeric polymer and aplurality of wings comprising the non-elastomeric polymer attached tothe core; quenching the fibers after they exit the capillary of thespinneret to cool the fibers, and collecting the fibers.
 15. The processof claim 14, comprising an additional step, after quenching, ofheat-relaxing the fiber so that it exhibits at least about 20%after-boil-off stretch.
 16. The process of claim 15, wherein theheat-relaxing is carried out with a heating medium of dry air, hot wateror superatmospheric pressure steam at a temperature in the range ofabout 80° C. to about 120° C. when the heating medium is said dry air,about 75° C. to about 100° C. when the heating medium is said hot water,and about 101° C. to about 115° C. when the heating medium is saidsuperatmospheric pressure steam.
 17. The process of claim 14, comprisingan additional step, after the quenching, of drawing the fiber so that itexhibits at least about 20% after-boil-off stretch.
 18. The process ofclaim 14, comprising an additional step, after the quenching, ofrelaxing the fiber by in the range of about 1-35% based on the fiberlength before relaxing.